It bugs me when they don't ask the question (in the past). Not the wee ones, of course. With them, I ask if they are here for "trick or treat", trying to encourage them to catch on to the proper procedure. And I always give the wee ones a large handful of whateven is on the go, regardless of what they say or don't say.

With kids about 7 or older, I quiz, "Yes?" And, with anyone who has a mustache or facial piercings (you get the idea), I say "Trick... and make it a good one for the security cameras." If they don't utter the magic words, I just shut the door.